The pavement marking industry has long been seeking improved types of raised retroreflective pavement markers. Raised markers, in contrast to other pavement markings such as painted lines, extend above the pavement so as to be visible and reflective even when the pavement is wet.
To be fully satisfactory, a raised retroreflective pavement marker should be applicable at low cost, should have a reasonably long useful life (which infers that it will maintain reflectivity, exhibit long adhesion to the roadway, and maintain physical integrity); should be nonhazardous if dislodged from the pavement surface; and should ideally remain on the pavement during snow-plowing. Despite a long period of effort on raised retroreflective pavement markers, and a measure of commercial success for some of them, no existing pavement marker has ever provided the desired combination of properties.